Recently, a mysterious bag of Doritos has been appearing on contestants' beds at The Biggest Loser ranch in Calabasas, CA. No one's been fingered yet, and perhaps more remarkable, no one's opened it, either. Or maybe that's not so surprising: This season — the seventh for the hit NBC weight-loss competition — has been a nail-biter, as the original 22 contestants have been fighting to out-lose one another in week after week of tense weigh-ins. They've been put through punishing workouts and special challenges. But all agree that their biggest test will come when they return home and face the temptations of their everyday lives. Here, four of the contestants talk about the diet difficulty that has most tripped them up in the past. And to help them, our experts, including the Good Housekeeping Research Institute's nutrition and food directors, offer smart solutions that anyone can use to become a successful loser.

Her fellow contestants see this former plus-size model as the biggest threat — she's been consistently among the top losers — which may be why they give Tara such a hard time. For a challenge that required pulling a two-ton car down the straightaway at California's Fontana speedway, the others wanted to make it even more difficult for her. "They added an extra 257 pounds to my car," Tara reports. Her trainer, Jillian Michaels, also tries to break her down, she says, to help her get to the bottom of her overeating. "I lost a career in modeling because I ate too much, and there was no one to blame but myself," she says. While some viewers are betting on her to win the $250,000 prize, Tara is focused on what comes next. "Now I want to reclaim my life."

At-Home Challenge: Nighttime snacking. "I took food to bed with me," Tara says. "A pint of Ben & Jerry's or a bag of Pepperidge Farm Milano Cookies and a glass of milk...I looked forward to it."

GH Strategies: A new routine — eating only in the kitchen, for example — will help Tara break that unhealthy practice, says GHRI Nutrition Director Samantha B. Cassetty, M.S., R.D. Then the trick is to replace the high-cal habit with a diet-friendly one. "As long as Tara's eating a satisfying diet and isn't starving at night, the new practice will start to feel routine quickly, in as little as two weeks," says Cassetty, who suggests that instead of cuddling up with a pint of ice cream (easily 1,000 calories) before she heads to bed, Tara might sip a 100-calorie cocoa nightcap, like the Heavenly Hot Chocolate from GHRI Food Director Susan Westmoreland.

Soon after she arrived at the ranch, Helen earned the nickname "Ma." One reason: She (along with Ron Morelli) is the go-to cooking instructor for younger contestants. "They were clueless," says Helen. "They'd make smoothies without putting the top on the blender! My own daughter" — Helen came with 29-year-old Shanon Thomas, who has since been eliminated — "once set her dinner on fire." Helen is also a bit of a devil. Following an episode that featured a "temptation" with Krispy Kreme donuts, the producers accidentally left behind a box. Helen placed three donuts on a plate by Tara's bed, with a note: "Good job today!" (Tara resisted.) But beneath it all, Helen isn't so sure of herself. When she got to the ranch, her self-esteem was so low, all she could think was, "Maybe I'll lose 10 or 20 pounds and then gain it back, like I've done my whole life." As she started working out, however, she was surprised by her own strength. "When you're as big as I was, your emotions shut down. Once you realize you're worth the effort, it's such a positive feeling." She had the ultimate payoff when Jillian, her trainer, told her she ran like an athlete. "Tears rolled down my cheeks, because I'd never been good enough to play sports, and I'd let all those opportunities pass me by," says Helen. "Now I want to go home and inspire other women my age — people who feel the way I used to."

At-Home Challenge: Cooking fun foods for her 17-year-old son and his friends on the football team. "I was the ultimate sports mom," Helen says. "I have a refrigerator in the garage stocked with soda and pizzas and hot dogs and burgers. I was the maniac chef for these boys, always having cookouts and making cookies and candy. But now I don't want to be tempted by those foods, and some of the boys who are heavy want me to help them lose weight, too."

GH Strategies: Since Helen and the team are frankfurter fans, we recommend she try one of the winners of our "Healthier Hot Dog Taste Test." Ball Park Lite Beef Franks, for instance, have 50 percent less fat and one-third fewer calories than most dogs, Cassetty points out. "If Helen's firing up the grill, I'd also suggest roasted fruits. Plums and peaches work well," says Cassetty. "And vegetables — even confirmed veggie haters have been converted when they tasted asparagus or peppers off the grill." The goal for Helen is to incorporate healthier choices into the same fun activities, like cookouts. For dessert? A leaner version of the cookout classic, s'mores: Place one roasted marshmallow on top of a 2.5-inch graham cracker square, and drizzle a teaspoon of chocolate syrup over it. Or serve with one Hershey's Bliss square (each s'more, about 90 calories).

It was when she and her husband began to talk about having a baby that Kristin realized she'd been in denial about her weight. "I just didn't feel safe about carrying a child," she says. Kristin started at the ranch with her mom, Cathy Skell, and since Cathy's elimination, she's missed being with family. "But it's been therapeutic. I can focus on how I got to be that person who weighed 360 pounds," which she still grapples with, says Kristin. Recently, she passed a milestone, becoming the first woman on the show to lose more than 100 pounds. "I can run now!" she says. "It started raining the other night, and I could literally run in out of the rain. Just to get out of bed in the morning and have a hundred fewer pounds crashing down on my ankles — everything's easier."

At-Home Challenge: Stress eating. "I have my own mortgage company," Kristin says. Given these tough financial times, she may well be tempted to turn to food when tension runs high. "My weakness is chocolate. Candy, cake, ice cream, cookies...anything chocolate."

GH Strategies: "Kristin got heavy because she didn't pay attention to herself," says Judith S. Beck, Ph.D., director of the Beck Institute for Cognitive Therapy and Research in Philadelphia. "Now she's going to have to make time for grocery shopping, for preparing meals and snacks to bring to work, and for exercise. She'll need to schedule each of these things in her planner until the behavior becomes automatic." Still, Beck adds, something may have to give if Kristin's schedule is crazy-busy. One strategy Beck uses with time-pressed clients is to have them think about what they could delegate, do less thoroughly, or drop altogether if they absolutely had to — say, if they had to go to the hospital every day for a blood transfusion. "That's when they realize they can find time for themselves," she says. As for Kristin's chocolate cravings, Cassetty suggests these low-cal options: No Sugar Added Fudgsicle (40 calories), Emerald Cocoa Roast Almonds Dark Chocolate Flavor 100 calorie pack, South Beach Living Snack Bar Delights in Chocolate Mint (100 calories). "The key is to set a limit of one treat a day," says Cassetty.

If Helen is "Ma," then Ron is the dad on the show. His support and tenderness are most apparent when he's relating to his 18-year-old son Mike, who came with him to the ranch and who's still on the show. Ron is also the kitchen "officer," always tidying up after the others. "They get annoyed because I wash a glass or knife as soon as someone sets it down," he admits.

Plagued by health issues — diabetes, a bleeding ulcer, and debilitating knee injuries — as well as years of yo-yo dieting (he has tipped the scales at 527 pounds), Ron underwent gastric-bypass surgery. It didn't work. Now he wants to succeed not only for himself but also for his wife and two sons. Mike is down 135 pounds so far, but 17-year-old Max is also overweight. "If I'd been able to tackle my weight when I was young, our lives would have been different," Ron says.

At-Home Challenge: Fast food takeout. "I was embarrassed to eat in front of people, so I did my bingeing when I was alone in my car," Ron says. "It automatically turned into every place with a drive-through window."

GH Strategies: "Given his health problems, Ron has a lot of reasons to want to keep losing weight. But to be successful, he's going to have to make a new rule: Only eat in the presence of other people," says Beck. "If he makes this decision and it's firm — no choice about it — he will eventually stop struggling with secret eating." He doesn't have to give up fast food, as long as he's with others (and picks healthy items). Beck has another suggestion to help Ron keep his resolve, especially during weak moments: "He should carry a 3" by 5" index card with him that says, 'I can eat in secret or I can continue to lose weight, but I cannot do both.' "